Lift Enhancement Of NACA0012 Using A Self-actuated Flexible Flap

Many researchers have paid lots of attention to the fundamental research on the aerodynamic performance of airfoil at different Reynolds number in the last decades,due to the rapid development and creative applications of UAV（Unmanned Aerial Vehicle/Drones）and MAV（Micro Aerial Vehicle）.Therefore,the enhancement of aerodynamic performance and flow control mechanism gains further development.It’s of great significant to develop the flow control technique to improve the aerodynamic performance of airfoil at post stall angle.In the present experiment,the passive control method of installing flexible flaps near the leading edge of the airfoil is used to explore the influence of flexible flaps on the aerodynamic performance of the airfoil.The time-averaged lift coefficient C_L,time-averaged drag coefficient C_D,lift-to-drag ratio C_L/C_D,and related flow field structure analysis are investigated in present work.The experimental Reynolds number（Re）is 1.5×10⁵,and the angle of attack of the airfoil ranges 0°～22°.The rectangular Pe（Polyethylene）films used in the present experiment are set with four different thicknessesδ（=0.0002c,0.0003c,0.0004c and 0.0005c）and seven different widths w（=0.025c,0.05c,0.075c,0.1c,0.125c,0.15c and 0.175c）,where c is chord length of airfoil.For lift and drag measurements,the films are installed at the leading edge of suction side of the airfoil,the distance from leading edge of airfoil is x_in（=0c,0.02c and0.05c）.In addition,to explore the influence of film material and shape on the aerodynamic performance of the airfoil,the experiment also used PET（Polyethylene terephthalate）film and two sawtooth shape Pe films with different serration heights h（=0.05c and 0.1c）for force measurement.PIV technology is used to study the aerodynamic mechanism of the lift enhancement of NACA 0012 airfoil by the films.Through the analysis of the experimental results,it is concluded that at Re=1.5×10⁵,and the control effect of the rectangular film is better than that of the sawtooth film.The optimal control case to obtain the maximum lift coefficient is that the rectangular Pe film with w=0.125c andδ=0.0004c is installed at x_in=0.02c,the stall angle is delayed from 12.5°to 18°,the maximum lift coefficient increasementΔC_L,max is30.18%,C_D decreased by 20.12%,and therefore C_L/C_Dincreased by 153.21%atα=18°.